#define _CRT_SECURE_NO_WARNINGS 1
#include<iostream>
#include<list>
using namespace std;

void test1()
{
	list<int> lt;
	lt.push_back(1);
	lt.push_back(2);
	lt.push_back(3);
	lt.push_back(4);


	lt.push_front(10);
	lt.push_front(20);

	for (auto e : lt)
	{
		cout << e << " ";
	}
	cout << endl;
}


int main()
{
	test1();
	return 0;
}